Axial Turbomachine Compressor Drum with Dual Means of Blade Fixing

ABSTRACT

The present application relates to a rotor drum of a low-pressure compressor of an axial turbomachine. The drum includes a wall generally symmetrical in revolution about an axis and following a generally curved profile. The wall is configured to support a plurality of blade rows. A first blade row is formed by an annular platform integrally formed with the wall at the peak of its profile in relation to the axis; and a second blade row directly downstream of the first; and a third blade row directly upstream of the first; are formed by one or more blade-retaining grooves formed on the wall. The first blade row and the drum form an integral assembly, eliminating certain vibrations. Anchoring the blades is hybrid or mixed. The rotor may be mounted in a housing with ring-shaped stators.

This application claims priority under 35 U.S.C. §119 to European PatentApplication No. 13173510.2, filed 25 Jun. 2013, titled “AxialTurbomachine Compressor Drum with Dual Means of Blade Fixing,” which isincorporated herein by reference for all purposes.

BACKGROUND

1. Field of the Application

The present application relates to a rotor of an axial turbomachine.More specifically the present application relates to a rotor drum of anaxial turbomachine compressor. The present application relates to anaxial turbomachine fitted with a low-pressure compressor rotor drum.

2. Description of Related Art

A turbomachine enables a gas to be compressed, burnt and expanded. Bythis means the turbomachine provides mechanical energy. To perform thesesteps, the turbomachine comprises a compressor and a turbine which arefitted with a rotor and a housing.

The inner surface of the housing and the outer surface of the rotordefine the contours of the primary flow path. It has variations in itsannular section. Its inner and outer contours can increase and decreasein diameter along the axis of the engine. In a compressor, especially alow-pressure one, the outer housing typically has a reduced diameterdownstream. Moving from upstream to downstream, the diameter of therotor may increase and then decrease. This combination of surfacesenables a wide inlet area and a high compression ratio at the output.

To transmit mechanical work to the fluid, the housing and the compressorrotor each comprise a plurality of annular rows of blades. The rotorblade rows and the stator blade rows alternate axially.

The housing may include a plurality of annular stators each comprisingan annular blade row. The stators form rings which abut each otheraxially for the purpose of assembling them. In this case, each blade inthe rotor row is attached to the rotor via a root inserted in an annulargroove formed on the rotor.

During assembly of a compressor with a drum-shaped rotor, a first bladerow is mounted on the rotor and then a stator is assembled axiallyfacing this first row. Only then can a second blade row be mounted onthe rotor after the stator relative to the first row. Assembly thuscontinues onwards, assembling a rotor blade row and a stator, one afterthe other. This mode of assembly is required by the fact that thestators being made in one piece and their inner diameters do not allowthe rotor with its blades to be inserted.

Patent FR 2845436 B1 discloses an axial turbomachine compressor. Thecompressor comprises an outer housing formed of several statorsassembled axially. It also comprises annular rows of blades which areeach located between the stators. The rotor blades are fixed by means ofroots that are inserted into annular grooves formed in the rotor. Thisembodiment makes it possible to produce a compressor that is simple toassemble. However, the rotor is subject to vibrations. It developscomplex vibrational modes that are difficult to analyse and damp.Moreover, its implementation requires complex and expensive machining.In addition, its structure is massive and heavy.

Although great strides have been made in the area of axialturbomachines, many shortcomings remain.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an axial turbomachine in accordance with the presentapplication.

FIG. 2 shows a diagram of a turbomachine compressor according to thepresent application.

FIG. 3 illustrates a section of the rotor drum according to the presentapplication.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present application aims to solve at least one of the problemspresent in the prior art. More particularly, the present applicationaims to reduce the vibrations in an axial turbomachine rotor. Thepresent application also aims to lighten the rotor of an axialturbomachine.

The present application relates to a rotor drum of an axialturbomachine, in particular of a low-pressure compressor, the drumcomprising a wall generally symmetrical in revolution about its axis andhaving a generally curved profile, the said wall being designed tosupport multiple rows of blades; wherein a first blade row is formed byan annular platform formed integrally with the wall at the peak of itsprofile with respect to the axis; and at least one, preferably every,second blade row directly downstream of the first and a third blade rowimmediately upstream of the first, is formed by one or moreblade-retaining grooves formed on the wall.

According to an advantageous embodiment of the present application, theouter surface of the retaining groove(s) is an average distance from theaxis which is less than the average distance of the platform from thefirst row to the said axis.

According to an advantageous embodiment of the present application, thewall comprises on its outer surface a set of annular ribs designed tomate with an annular layer of abradable material so as to provide aseal, the set of annular ribs being located axially between the firstand second blade rows and/or between the first and third blade rows.

According to an advantageous embodiment of the present application, theminimum distance of the peaks of one set of ribs with respect to theaxis is greater than the maximum distance from the said axis to theouter surface of the adjacent retaining grooves. It is the groove(s) ofthe second and/or third row blade row(s).

According to an advantageous embodiment of the present application, theblades of the first row are welded to the platform of the said row.

According to an advantageous embodiment of the present application, theplatform of the first blade row comprises blade stubs on which arewelded blade extensions; preferably the height of the blade stubs ismore than 10% of the radial height of the blades in the first row, morepreferably more than 25%.

According to an advantageous embodiment of the present application, theblades of the first row are at least partially cut into the body of theunmachined drum.

According to an advantageous embodiment of the present application, thegeneral curved profile of the wall extends over most of the length ofthe drum and/or has a main concavity directed towards the main axis andextending over the major part of the length of the drum, the saidprofile having a radius relative to the axis which is at a maximum atthe first blade row.

According to an advantageous embodiment of the present application, theplatform of the first blade row is raised relative to the wall directlyupstream and downstream of the said row.

According to an advantageous embodiment of the present application, thewall comprises two parts extending generally radially under the platformof the first row, so that the longitudinal section of the wall at thesaid platform has a π-shaped profile.

According to an advantageous embodiment of the present application, thewall comprises at least one annular stiffener extending radiallyinwardly at the first blade row, preferably in the extension of at leastone of the radial parts.

According to an advantageous embodiment of the present application, thewall directly upstream and downstream of the first row comprises a partwith substantially constant thickness which defines an annular space forhousing a stator inner shell.

According to an advantageous embodiment of the present application, therotor drum comprises blades of the second and/or third blade row, eachof the said blades comprising a root housed in the, or a, retaininggroove.

According to an advantageous embodiment of the present application, theretaining groove(s) is/are annular along the perimeter of the drum.

According to an advantageous embodiment of the present application, theblades in the first row and the annular platform form an integral unit.

According to an advantageous embodiment of the present application, thedrum is made of a metallic material, preferably titanium.

According to an advantageous embodiment of the present application, thewall is forged and machined from solid.

According to yet another advantageous embodiment of the presentapplication, the annular platform and the retaining grooves areintegral.

According to an advantageous embodiment of the present application, thedrum shows material continuity between the first row blades and thewall.

According to an advantageous embodiment of the present application, aset of annular ribs is distributed axially over the annular junction.

According to an advantageous embodiment of the present application, allthe drum blade rows, except the first, comprise a blade-retaining groovefor the purpose of assembling them on the drum.

The present application also relates to an axial turbomachine comprisinga rotor drum, wherein the drum is in accordance with the presentapplication; preferably the rotor is a low-pressure compressor rotorcomprising essentially three annular rotor blade rows.

The present application also aims to reduce the vibrations of an axialturbomachine rotor. To achieve this, it removes any freedom of movementbetween the annular wall and the blades in the first row. The presentapplication also improves the overall rigidity of the drum. The proposedarchitecture also enables the rotor to be lightened, affecting both thedrum and the blades.

Machining the surfaces of the drum and the blades is simplified. All ofthese improvements to the drum are possible while maintaining thecompatibility of the rotor with a housing formed of annular stators.

The present application is applied to a drum provided with annular ribsused as a means of sealing between the compression stages. This aspectis not limiting since the present application may also be applied to adrum mating with axial brush seals. Such seals are well known to thoseskilled in the art and may, for example, correspond to those disclosedin Patent DE 102005042272 A1.

In the following description, the terms inner or internal and outer orexternal refer to a position relative to the axis of rotation of theaxial turbomachine.

FIG. 1 shows a schematic view of an axial turbomachine. In this case itis a double-flow turbojet. The turbojet 2 comprises a first compressionstage, a so-called low-pressure compressor 4, a second compressionstage, a so-called high-pressure compressor 6, a combustion chamber 8and one or more turbine stages 10. In operation, the mechanical power ofthe turbine 10 is transmitted through the central shaft to the rotor 12and drives the two compressors 4 and 6. Reduction mechanisms mayincrease the speed of rotation transmitted to the compressors.Alternatively, the different turbine stages can each be in communicationwith the compressor stages through concentric shafts. These lattercomprise several rotor blade rows associated with stator blade rows. Therotation of the rotor around its axis of rotation 14 generates a flow ofair and gradually compresses it up to the inlet of the combustionchamber 10.

An inlet fan, commonly designated a fan 16, is coupled to the rotor 12and generates an airflow which is divided into a primary flow 18 passingthrough the various above-mentioned levels of the turbomachine, and asecondary flow 20 passing through an annular conduit (shown in part)along the length of the machine which then rejoins the main flow at theturbine outlet. The primary flow 18 and secondary flow 20 are annularflows and are channeled through the turbomachine's housing. To this end,the housing has cylindrical walls or shells that can be internal orexternal.

FIG. 2 is a sectional view of a compressor of an axial turbomachine 2such as that shown in FIG. 1. The compressor may be a low-pressurecompressor 4. The teaching of the present application may also beapplied to the rotor drum of a turbine 10.

A splitter nose 22 of the primary 18 and secondary 20 airflows can beseen on the compressor 4. The rotor 12 comprises a plurality of annularrotor blade rows; in the case of FIG. 2 there are three. Further bladerows can be provided for. These three rows are axially consecutive.There is a first row of rotor blades 24, a second row of rotor blades 26downstream of the first row 24 and a third row of rotor blades 28upstream of the first row 24.

The rotor blades (24, 26, 28) spread out substantially radially from therotor 12. The blades in one row are regularly spaced from each other,and have the same angular orientation to the airflow. Optionally, thespacing between the blades can vary locally as can their angularorientation. Some blades in a row may be different from the rest.

The compressor 4 comprises an external housing. The outer housingcomprises several stators, for example four, which each comprise anouter shell 30, a stator blade row 32 and, optionally, an inner shell34. An annular layer of abradable material 36 may be applied to theinside of the outer shell and the inner shell of a stator. The statorblades 32 of the same stator extend radially from their outer shell 30towards their inner shell 34. The stators form closed circular rings.They are assembled axially against each other and fixed to each other bymeans of radial flanges 38.

The stators are associated with the fan or a row of rotor blades (24,26, 28) for straightening the airflow so as to convert the speed of theflow into pressure.

The rotor 12 comprises a drum 40. The drum 40 has a wall 42 generallysymmetrical in revolution about its axis of rotation 14, which axis iscommon with that of the turbomachine. The wall 42 may have an overallprofile of revolution or the average profile of revolution about theaxis of rotation 14. The general profile can be included in thethickness of the parts of the wall 42 that are axially at right anglesto the stator blade rows.

The general profile is basically curved and may have a continuouscurvature and/or continuously varying curvature. Radially it matches thevariation in the inner surface of the primary flow 18. The exterior ofthe general profile is convex. Going from upstream to downstream theradius of the inner surface increases and then decreases, so that theprofile of the wall has a maximum. The wall 42 is basically thin. Itsthickness is generally constant. Its thickness is less than 10.00 mm,preferably less than 5.00 mm, more preferably less than 2.00 mm. Thewall 42 forms a hollow body which defines a cavity having a shape of anogive or keg. The drum 40 and/or the rotor blades (24, 26, 28) are madeof a metallic material, preferably titanium.

The drum 40 comprises annular ribs 44 or lip seals. They form narrowannular strips which extend radially. They are designed to mateabrasively with annular layers of abradable material 36 on a stator soas to provide a seal. Generally, one abradable layer 36 mates with twoannular ribs 44.

FIG. 3 is a detailed sectional view of the drum 40 of FIG. 2. The drumcan also be a rotor drum of a high-pressure compressor. It can possiblyalso be a turbine rotor drum.

The first blade row 24 is integrally formed on the wall by an annularplatform 46. The annular platform 46 is integrally formed with the wall42. The annular platform 46 is formed atop the profile of the wall 42.The annular platform 46 has a profile of revolution generally straightor substantially curved.

The rotor blades 26 of the second row and the third row 28 each includea blade platform 48 defining the inside of the primary flow, a blade 50extending radially outwardly from the blade platform 48, and a retainingroot 52 extending radially inwardly from the blade platform 48. Theretaining root 52 may be dovetailed. It may have a form whose axialdimension increases as it gets closer to the inside, enabling it to lockin place.

The wall 42 of the drum 40 comprises two zones for fixing blades usingretaining grooves. The fixing zones each comprise an annular groove 54into which the retaining roots 52 of the second-row blades 26 and thethird-row blades 28 are inserted. The annular grooves 54 compriseannular outer surfaces which come into contact with the blade platforms48. The blade platforms 48 of the second blade row 26 engage with thesecond outer surface 56, and the blade platforms 48 of the third bladerow 28 engage with the third outer surface 58.

The retaining roots 52 generally have a shape matching the correspondingretaining groove so as to ensure radial retention. The retaining grooves54 have a profile with a constriction at their outer face. Thus, thesecond row blades 26 and the third row blades 28 are retainedreversibly. Mechanical clearance is provided between the annular wall 42and the rotor blades of the second and third rows, so as to allow slightmovement of the blades. However, the rotor is designed so that thecentrifugal forces present during the compressor's operation force theblades into position in their throats.

According to an alternative of the present application, the retaininggrooves can be axial grooves. The annular wall then comprises an annularrow of axial grooves distributed over its circumference, and which eachform an annular blade row.

The outer surface (56, 58) of at least one of the annular grooves 48 isat an average distance from the axis 14 which is less than the meandistance between the annular platform 46 and the first row 24 of thesaid axis. Preferably, each radius at an axial end of the annularplatform 48 is greater than the maximum radius of the outer surface (56,58) located opposite.

The first row blades 24 are anchored to the drum in a different mannerfrom those of the other rows (26, 28). The blade retention or attachmentis heterogeneous or hybrid. The first row blades 24 are fixed by weldingto the annular platform 46. They may be welded by friction, for exampleby a process of orbital welding. The drum 40 thus serves as a supportfor fixing both types of blades.

For this purpose, the blades corresponding to the first row 24 areattached to a bare drum and welded to the annular platform 46. Theseblades can be directly or indirectly fitted onto the annular platform46. The annular platform 46 may include blade stubs 60 extendingradially from its outer surface. In this case, each blade which iswelded to the second surface effectively forms a radial portion of thefinal blade. The weld 62 between a stub and a blade portion is set abovethe annular platform 46.

According to an alternative of the present application, the first rowblades 24 can be integrally machined into the body of the unmachineddrum in which the wall is also machined.

Thus, the wall of the drum 40 and the first row blades form an integralunit. They show continuity of material. Their metallic materials havecrystalline continuity at their interface. They can, at least partially,be formed integrally. Anchoring the blades is irreversible. The firstrow blades 24 are integral with the annular wall 42. This embodimenteliminates vibration between the first row blades 24 and the wall 42 ofthe drum 40.

In addition, this method of anchoring the blades simplifies themachining to be carried out because the annular platform 46 and anystubs 60 are simpler to produce than an annular groove or a plurality ofaxial grooves. Indeed, a groove must be cut in a generally inaccessiblespace with a small tool, which increases the manufacturing time.Alternatively, an axial groove can be machined by broaching. However,this method for removing material requires expensive tooling and is notsuitable for all types of drum.

The wall 42 of the drum immediately upstream and downstream of the firstblade row 24 comprises at least a part 64 of substantially constantthickness or an axial annular join 64, with preferably two parts ofsubstantially constant thickness 64. Each constant thickness part 64extends axially from the annular platform 46 to the second blade row 26or to the third blade row 28. The annular platform 46 is radially setout from the constant thickness part 64. The constant thickness parts 64define an annular space between the first blade row 24 and the secondblade row 26 or the third blade row 28, the annular spaces beingradially open outwards. They are designed to accommodate the internalstator shells.

The wall 42 comprises two parts 65 which extend generally radially. Theyextend from the annular platform 46 inwardly. They may be located ateach one of the axial edges of the annular platform 46. Thus, the wallmay have a generally π-shaped profile. The profiles of the radialportions extend generally perpendicular to the profile of the annularplatform 46.

The annular ribs 44 are located on the constant thickness parts 64. Eachset of ribs comprises a plurality of ribs 44. On each side of theannular platform 46 there are progressive decreases in the externalradii from an edge of an annular platform 46, ribs 44, and outersurfaces (56, 58) of the annular grooves. The peaks of these elementsform a staircase. This configuration enables bladed stators to be fixedon both sides of the first blade row 24, and then the second row 26 andthe third row 28 to be assembled.

FIG. 3 shows the blades 32 and the inner shell 36 of the two statorsupstream and downstream, respectively, of the first blade row 24. FIG. 3also illustrates with dashed lines these stators in an intermediateposition during axial assembly around the drum.

The annular wall 42 of the drum includes annular stiffeners 66. Theannular stiffeners 66 may include annular flanges which extend radiallyinwardly. These flanges are located axially at the ends of the annularplatform 46, preferably in the radial extension of the radial portions65.

The drum is usually machined by turning starting from an unmachineddrum-shaped blank of which the walls include the finished drum. The drumblank must radially encompass the outer surfaces of the annular grooves54, the annular platform 46, the internal stiffeners 66, and any bladestubs 60. Depending on circumstances, it may include the first blade row24 along the entirety of their radial height.

I claim:
 1. A rotor drum of an axial turbomachine, comprising: a wallgenerally symmetrical in revolution about an axis thereof and having agenerally curved profile, the wall being configured to support aplurality of blade rows; a first blade row formed by an annular platformintegrally formed with the wall at a peak of the profile thereof inrelation to the axis; and at least one second blade row directlydownstream of the first blade row and a third blade row directlyupstream of the first blade row, the second blade row being formed byone or more blade-retaining grooves formed on the wall.
 2. The rotordrum in accordance with claim 1, wherein the outer surfaces of theretaining grooves are at an average distance from the axis which is lessthan the average distance from the platform of the first row to theaxis.
 3. The rotor drum in accordance with claim 1, wherein the wallcomprises: a set of annular ribs on the outer surface of the wallconfigured to mate with an annular layer of abradable material, so as toprovide a seal, the set of annular ribs being located axially betweenthe first blade row and the second blade row and between the first bladerow and the third blade row.
 4. The rotor drum in accordance with claim1, wherein the wall comprises: a set of annular ribs on the outersurface of the wall configured to mate with an annular layer ofabradable material, so as to provide a seal, the set of annular ribsbeing located axially between the first blade row and the second bladerow or between the first blade row and the third blade row.
 5. The rotordrum in accordance with claim 3, wherein the minimum distance of thepeaks of one set of ribs relative to the axis is greater than themaximum distance from the axis of the outer surfaces of the adjacentretaining grooves.
 6. The rotor drum in accordance with claim 1, whereinthe blades of the first blade row are welded to the platform of thefirst blade row.
 7. The rotor drum in accordance with claim 1, whereinthe platform of the first blade row includes blade stubs on which arewelded blade extensions, the height of the blade stubs being more than10% of the radial height of the first blade row.
 8. The rotor drum inaccordance with claim 1, wherein the platform of the first blade rowincludes blade stubs on which are welded blade extensions, the height ofthe blade stubs being more than 25% of the radial height of the firstblade row.
 9. The rotor drum in accordance with claim 1, wherein theblades of the first blade row are at least partially cut into the bodyof the unmachined drum.
 10. The rotor drum in accordance with claim 1,wherein the general curved profile of wall extends over most of thelength of the drum and has a main concavity directed towards the mainaxis and extending over the major part of the length of the drum, theprofile having a radius relative to the axis, which is at a maximum atthe first blade row.
 11. The rotor drum in accordance with claim 1,wherein the general curved profile of wall extends over most of thelength of the drum or has a main concavity directed towards the mainaxis and extending over the major part of the length of the drum, theprofile having a radius relative to the axis, which is at a maximum atthe first blade row.
 12. The rotor drum in accordance with claim 1,wherein the platform of the first blade row is raised relative to thewall directly upstream and downstream of the first blade row.
 13. Therotor drum in accordance with claim 12, wherein the wall comprises: twoparts extending generally radially under the platform of the first bladerow, so that the longitudinal section of the wall at the said platformhas a π-shaped profile.
 14. The rotor drum in accordance with claim 13,wherein the wall comprises: at least one annular stiffener extendingradially inwardly at the first blade row in the extension of at leastone of the radial parts.
 15. The rotor drum in accordance with claim 13,wherein the wall immediately upstream and downstream of the first bladerow comprises: a substantially constant thickness part which defines anannular space for accommodating a stator inner shell.
 16. The rotor drumin accordance with claim 1, further comprising: blades of the secondblade row and the third blade row, each of the blades comprising: a roothoused in a retaining groove.
 17. The rotor drum in accordance withclaim 1, further comprising: blades of the second blade row or the thirdblade row, each of the blades comprising a root housed in a retaininggroove.
 18. The rotor drum in accordance with claim 1, wherein theretaining grooves are annular along the perimeter of the drum.
 19. Anaxial turbomachine, comprising: a rotor drum, comprising: a wallgenerally symmetrical in revolution about an axis thereof and having agenerally curved profile, the wall being configured to support aplurality of blade rows; a first blade row formed by an annular platformintegrally formed with the wall at a peak of the profile thereof inrelation to the axis; and at least one second blade row directlydownstream of the first blade row and a third blade row directlyupstream of the first blade row, the second blade row being formed byone or more blade-retaining grooves formed on the wall; wherein therotor drum is a low-pressure compressor rotor having essentially threeannular rows of rotor blades.